Serum or plasma concentration of immunoglobulin G (IgG) antibodies against *Pneumocystis jirovecii* (PCP) antigens, measured by immunoassay

Your doctor may order this test to help find out what is causing your symptoms, to confirm or rule out a suspected condition, or to monitor how a known health problem is responding to treatment. It can also be part of a routine checkup or a screening when you have certain risk factors, helping your care team make informed decisions about your health.

Your healthcare provider may recommend this test if you have a weakened immune system (e.g., due to HIV/AIDS, chemotherapy, or other immunosuppressive conditions) and are at higher risk for PCP. It may also be used in research or specialized clinical settings to study immune responses to PCP.

A positive result usually means that the substance, condition, or abnormality the test was designed to detect was found in your sample. Depending on the test, this could point to an infection, a disease, or another health issue that needs attention. Your doctor will review the result together with your symptoms, medical history, and any other testing to decide what it means for you and whether further evaluation or treatment is needed.

A positive result indicates that your body has produced antibodies against *Pneumocystis jirovecii*, suggesting past exposure or immunity. However, it does not confirm an active infection—other tests (like a sputum culture or bronchoscopy) may be needed to diagnose current PCP.

A negative result generally means that the test did not detect the condition or substance it was looking for. In many cases this is reassuring, but no test is perfect, and a negative result does not always completely rule out a problem, especially if it was done too early in the course of an illness. If your symptoms continue, your doctor may recommend repeat testing or additional tests to look for another explanation.

A negative result means your blood did not detect IgG antibodies against PCP at the time of testing, which could mean you have never been exposed or have low immunity. This does not rule out an active infection, so further evaluation may still be needed.

The way this test is performed depends on the type of sample or measurement it requires. Many laboratory tests use a small blood sample drawn from a vein in your arm, while others use a urine sample, a throat or nasal swab, or imaging. The procedure is usually quick and is done in a doctor's office, clinic, or laboratory, and a trained healthcare professional will explain each step and help you stay comfortable throughout.

A blood sample is drawn from a vein in your arm. The serum or plasma is then tested in a lab using an immunoassay method to measure antibody levels against PCP antigens.